There is a maxim that four quarts of clean oil mixed with one quart of dirty oil makes five quarts of dirty oil. In the area of fluid filtering apparatus and related filtering applications, this is especially true. Modern vehicles and industrial machinery rely on a number of recirculating fluids for effective operation. Effective filtration of these fluids can extend the life of the apparatus and maintain the operation at high levels of performance. Furthermore, to the extent fluids can be maintained free of contamination, the life of the fluid itself is extended, saving cost due to fluid replacement and machinery downtime.
One particularly effective type of fluid filter causes fluids to flow interstitially between layers of fibrous tissue which have been wound about an inner core. Such fluid filters may be packaged either as disposable canisters, replaceable cartridges, or as containers for containing generally one or more filter elements. In-flow and out-flow connections provide the container's inlet and outlet ports. By flowing interstitially between the layers of filtering tissues, dirt and smudge is removed from the fluid by the tissue layers. The fluid exits the filter element and then is directed by a fluid collector through passageways to a flow path which is fluidicly connected to the outlet port.
Because of the efficiency and quality of wound fibrous tissue filtering systems, the popularity of such systems has increased. However, this popularity has not been without a need to improve the various sealing areas of the filtering tissue systems. For instance, because the filtering fluid typically flows interstitially and not transversely through the wound media, a problem known as "channeling" can occur. Channeling typically has the effect of short circuiting the filtering process. It may occur, for instance, due to localized high pressures that open the space between wound layers of fibers such that a larger portion of unfiltered fluid may pass. Furthermore, in using these and other types of filters, other leakages can occur. For instance, leakages can occur around the ends of the filtering elements such that unfiltered fluid from an unfiltered flow path leaks into a filtered flow path and contaminates what fluid was actually filtered. Thus, it is critical to seal the unfiltered fluid from the filtered fluid.
Another example relates to the use of multiple filter element in a filtering system. To increase the flow through a filtering system, it is often desirable to provide a plurality of stacked tissue elements to minimize flow resistance. However, the junctions between the multiple elements is prone to leakage of unfiltered fluid into filtered fluid. To reduce this problem, a fluid collector is typically used.
A typical fluid collector serves to seal the end of the filter element from leakage of unfiltered fluid to filtered fluid. In multiple tissue element systems, it may also separate the fibrous tissue rolls from one another and provide passage for filtered fluid to leave the filter element. Fluid collectors, generally known in the art, may be formed which may have a plurality of alternating radial slots and ridges with the ridges serving to space the fibrous tissue roll elements from the collector and the slot serving to direct the filtered fluid into a central flow tube. A separate fluid collector may be used or the function of a fluid collector may be built into a container. Typical materials include various hard plastics known to those in the art such as Delrin 500, nylon, or other suitable materials.
A further complication of using wound fibrous layers is from the differential pressure generated from the unfiltered flow path to the filtered flow path. Typically, the unfiltered flow path will have a higher pressure than the pressure of the filtered flow path due to the pressure drop through the fluid filter. This differential pressure may create extra stress on the fibrous layers and overall compress the layers away from the higher pressure, typically, toward the inner core and the filtered fluid path. These substantial compressive forces are described in U.S. Pat. No. 4,792,397 to Rasmussen in column 1, lines 35-49 as follows:
Substantial compressive forces are exerted hydraulically on the tissue layers. These forces tend to compress and deform the filter elements, particularly at the end of each filter element where the filter fluid exits into a collector. As disclosed in U.S. Pat. No. 4,017,400 to Schade, these collectors often have an annular portion which extends into the adjacent filter element ends to form a seal which separates the filtered fluid from the unfiltered fluid. Nevertheless, deformation of the filter element at its exit end may cause flow channels to form which then allow fluid to flow around the annular seal and thus entirely bypass the filter element. As a result, a significant amount of unfiltered fluid can pass around the deformed filter element without removal of contaminants. PA1 A significant problem associated with the use of axial flow filters has been leakage of contaminated fluid around the wound tissue filter element. Ordinarily, filter elements are positioned on a flow tube and contaminated fluid is directed to one axial end surface of the element where the fluid enters the tissue layers in an axial direction, flows through the layers, and out the opposite axial end surface of the element into an annular channel then into the flow tube. The pressure differentials between the axial ends of the element, and between the outer cylindrical surface of the elements and the annular channel are typically very high, encouraging leakage around the elements, permitting unfiltered fluid to contaminate the filtered fluid. Numerous attempts have been made to fashion a seal which will prevent a flow bypass of this type. PA1 Bypassing is precluded in the apparatus of this invention by squeezing the filter cartridge from top and bottom between circular stub edges to indent the cartridge faces so tightly that no fluid can flow regularly to the axial bore or the outflow pipe without proceeding axially through one-half of the dual cartridge. PA1 An interlocking annular seal provided in the manner of this invention is enhanced in efficiency by application of radial pressure and will resist failure under extreme pressure better than seals formed by axial compression of a filter element or by an annular sealing ring which causes the filter element to be squeezed and deformed radially. PA1 However, it has been discovered that even with such an annular seal, the great hydraulic forces within the filter still results in deformation of the filter element. This causes flow channels to form which allow fluid to flow around the annular seal and thus bypass entirely the filter element. The result is that a significant amount of unfiltered oil is recirculated without removal of much of the contaminates.
Obviously, in using these wound fibrous tissue filter elements, such leakage can occur from using one or a plurality of such filter elements in any given system. As is noted in U.S. Pat. No. 4,773,990 to Hood in column 1, lines 24-42:
In recognizing some of the problems, various inventors have suggested solutions. One such solution is seen in U.S. Pat. No. 271,850 to Stutzman. In that patent, reduction of leakage bypassing is discussed in terms of axial compression in column 5, lines 18-23:
However, other inventions realize that there is a practical limit to how tight the actual ends can be squeezed to reduce leakage and perhaps rely instead on other methods of sealing.
U.S. Pat. No. 4,017,400 to Schade appears to attempt to find a solution in sealing the outer periphery of the filter element against the container wall and providing an "interlocking annular seal" in column 1, line 64--column 2, line 2.
Noteworthy, this was a single ring which apparently attempted to restrain the filter element from pulling away from the inner container wall surface. Unfortunately, Schade and others apparently realized subsequent to this patent that this was not a final solution.
While the Schade '400 reference may have recognized an issue of radial compression, it apparently did not offer a satisfactory solution. In U.S. Pat. No. 4,366,057 to Bridges et. al., the Schade '400 reference is described. As a background, that reference indicates that a "pressure drop across the filter may be in excess of 90 P.S.I., resulting in substantial compressive forces being exerted hydraulically on the filter tissue. These forces tend to compress and distort the filter element, particularly at the return or exhaust ends thereof." (Column 1, lines 33-38). Then, the Bridges '057 reference describes that the Schade '400 reference provided an interlocking annular seal inserted into the filter element a few layers inwardly of the perimeter of the filter element. The Bridges '057 reference continues in stating in Column 1, lines 45-52,
U.S. Pat. No. 4,773,999 to Schade, approximately eleven years later after the Schade '400 reference, noted that "provision of an effective seal about the outer periphery of the outflow gallery is especially problematic because the configuration of the wound tissue rolls tend to distort under the effects of the differential pressure and the rolls tend to be compressed so as to pull away from less conformable sealing means, . . . " (Column 1, lines 19-25). The Schade '999 reference attempted to solve the earlier problems by providing a seal "between filter elements by wrappings of filter medium tissue being applied around the outer peripheral surfaces of the elements to at least partially encase such surfaces and completely overlap the space between the elements which comprises the filtrate overflow gallery." (Column 1, lines 48-54) In other words, it appears that Schade attempted to solve the sealing problems by providing an outer "sock" that overlaps the gap between multiple filter elements, with the inference from the Schade '999 reference that interstitial sealing by flow collectors and similar devices was ineffective.
The next generation of improvements in attempting to better seal against this type of leakage is perhaps found is U.S. Pat. No. 4,780,204 to Rasmussen assigned to Harvard Corporation of Evansville, Wis. Among other things in that reference, the concept of placing an annular ring portion inwardly a few tissue layers was extended to allow a taper to a sharp edge to more easily push the fluid collector between the layers of filtered tissue of adjacent filter element ends without damaging the tissue. (Column 5, lines 27-32) However, even with this improvement, some additional improvement was needed.
Another improvement is seen in U.S. Pat. No. 4,792,397 to Rasmussen and assigned to Harvard Corporation. In that reference, two outer rings in proximity to each other appear to be disclosed. One ring does not appear to engage the interstitial layers, but is located on the outside of the layers of tissue with an overlapping sheet made from a material typically known under the trademark "Mylar" to attempt to seal the intersection of the ends of the two filter elements. A second ring is located proximate to the outer ring and appears in functional similarity to the ring of the Rasmussen '204 reference. The Rasmussen '397 reference attempted to restrict the outer movement of the tissue layers in the filter and avoid compressing the filter against the container wall causing difficult removal. This perhaps was a problem in the Schade '400 reference where the filter element may have become lodged against the container wall and difficult to remove. However, the Rasmussen '397 reference does not appear to have accounted for circular inconsistencies in the outer periphery of a wound filter element. For instance, if the filter element were wound in an oblong fashion, one of the two seals, if not indeed both of them, might escape interstitial sealing against the wound layers.
Thus, the field of the present invention is such that economics and efficiency are realized by using wound tissue layers. However, the need still exists for improved leakage control both between the wound tissues of layers as well as around the sealing ends of the filter elements.
Ironically, the development and filtration and improvements in leakage control have prompted the emergence of previously unencountered or unnoticed weaknesses in the filtration system. That is, the more tightly sealed filter elements have been found, on occasion, to develop axial flow bypass channels down through the filter elements themselves. These bypass channels may result in direct, substantially uninhibited, flow communication between the fluid entry surface and the fluid exit surface by allowing unfiltered fluid to completely escape filtration. This unexpected occurrence has presented new problems for filter manufacturers and developers. Thus, as various problems have been solved, other problems have developed. The technology has seen an increase of the need for further leakage control. The present invention fulfills this extra need.
Part of the problems remaining from prior endeavors appear to be caused by not realizing the real world aspects of manufacturing wound tissue filter elements. Pictorially, this is represented in FIG. 1. As can be seen, the outer circle could be a container wall (14), ring, and so forth. The inner circle could be a ring such as disclosed in the above-references. In some instances, the ring could engage interstitially a portion of the filtering medium between the tissue layers (area A). In some instances, the engagement could be minimal (area B) and in other instances perhaps not at all (area C). Thus, unfiltered fluid, in seeking the path of least resistance, could seek out the minimal or no engagement areas and leak past the rings into the filtered flow path and contaminate the filtered fluid. The present invention, at least in one goal, seeks to remedy this apparent deficiency.
Another aspect that may have been realized by some inventors and yet not apparently fully resolved is shown in FIG. 2. An unfiltered flow path (12) containing the unfiltered fluid typically flows between the container walls (14) and the original outer periphery (15) of a filter element. However, because of pressure differences between the unfiltered flow path (12) and the filtered flow path (12a), a hydraulic flow force (16) may be directed against the filter element and may compress the wound layers of tissue (22). This compression may move the original outer periphery (15) to a new resulting outer periphery (17) of the filter element after the hydraulic flow force compresses the element. Because the hydraulic flow force may be strong, this may drive unfiltered fluid through a leakage channel (18a) into the filtered flow path (12a) and contaminate the filtered fluid.
FIG. 3 shows an improvement by using at least two rings, one non-interstitial ring (15a) and a single interstitial ring (15b). However, as described in FIG. 2, it appears that the hydraulic flow force (16) may also force leakage in a similar manner as in FIG. 2. This may occur for at least two reasons. First, by using a non-interstitial outer ring, the difficulty of varying thickness (as described in FIG. 1), does not assure an engagement of a sufficient amount of wound layers of tissue (22) between the non-interstitial ring (15a) and single interstitial ring (15b). Thus, the hydraulic flow force may likewise drive unfiltered fluid along the similar leakage channel (18a). A second reason is that there may be a hydraulic flow force that forces the wound layers of tissue (22) on the inside circumference of the single interstitial ring (15b) such that a non-engaged area (18) appears. It may be that this was originally thought to be a seal but appears ineffective because of the hydraulic flow force (16) compressing the layers away from this ring or perhaps other reasons.
Thus, of the solutions found and reviewed, a need still exists for more effective sealing. The present invention fills this gap. While the needed implementing arts and elements have long been available, and a long felt need has existed, no invention appears to have accomplished the goals and objects of the present invention. Certainly, those in the field appreciated that a problem existed and that the problem involved leakage, but were unable to fully appreciate the solution to the problem. As seen above and in other areas, substantial attempts were made by those skilled in the art to fulfill the needs or to cope with the difficulties, but they either failed to appreciate the fill scope of the problem or only provided a partial solution. Part of this realization may have been a failure to understand the real world complexities of producing satisfactory shaped filters of the quality needed, considering the expense involved. Thus, the present invention seeks to resolve these issues and provide a simple and economical apparatus and method.